Method of liquid phase sintering a two-phase alloy

ABSTRACT

Liquid phase sintering method for a two-phase alloy includes forming a green body billet of a two-phase alloy, solid state sintering the green body billet, surrounding the solid state sintered billet with a refractory barrier medium within a refractory container to form a charge, optionally flowing wet hydrogen through at least a portion of the charge, equilibrating a charge temperature below a solidus temperature of the two-phase alloy, changing the charge temperature to a liquid phase sintering temperature of the two-phase alloy, maintaining the liquid phase sintering temperature for a period of time of ≦four hours, reducing the charge temperature to less than the solidus temperature of the two-phase alloy, and optionally holding the charge stationary as the charge temperature passes through the solidus temperature. Optionally, the charge can be rotated about an axis of symmetry during liquid phase sintering and a portion of the charge can be zone heated.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0001] At least some aspects of this invention were made with Governmentsupport under contract no. F08630-96-C-0042 DMCPW. The Government mayhave certain rights in this invention.

BACKGROUND

[0002] The present invention relates to liquid phase sintering of atwo-phase metal alloy. More particularly, the present invention relatesto a method to liquid phase sinter a tungsten heavy alloy.

[0003] Large size and/or geometrically complex two-phase alloymaterials, such as tungsten heavy alloy (WHA), are difficult to produceas a single piece.

[0004] Liquid phase sintering (LPS) can be used to produce WHA parts.However, LPS can be limited by, for example, maximum furnace size,severe slumping of parts, liquid matrix runout of WHA material, andsubstantial compositional variation due to alloying elements, such astungsten in WHA, settling under gravity. Further, long process times attemperatures where liquid matrix is present can exacerbate thelimitations. For example, LPS processes can include up to 14 to 20 hoursat greater than 1475° C., resulting in settling of the tungsten grainstoward the bottom of the part and/or the formation of a portion of thepart that is matrix rich.

[0005] Current methods of producing large pieces include liquid phasesintering in a pusher furnace. A pusher furnace LPS process can includepushing a WHA billet at a given rate through a hot zone of a longfurnace with an essentially fixed temperature profile along the length.However, part size in a typical pusher furnace LPS consolidation processcan be limited by the furnace opening, which is approximately 20 incheswide and 4 inches high. Further, tungsten particle settling can occur ina WHA billet higher than four inches when processed in a pusher furnacedue to gravity during the time when the matrix of the material isliquid. This can be especially pronounced in thicker WHA parts, whichcan show compositional variations of up to 10 weight percent (wt. %) ormore in the part.

SUMMARY

[0006] An exemplary liquid phase sintering method for a two-phase alloycomprises forming a green body billet of a two-phase alloy, solid statesintering (SSS) the green body billet, forming a charge by surroundingthe solid state sintered billet by a refractory barrier medium within arefractory container, wherein the refractory barrier medium preventscontact between the solid state sintered billet and the refractorycontainer, equilibrating a temperature of the charge below a solidustemperature of the two-phase alloy, changing the temperature of thecharge to a liquid phase sintering temperature of the two-phase alloy,maintaining the liquid phase sintering temperature for a period of timeof less than or equal to four hours, and reducing the temperature of thecharge to less than the solidus temperature of the two-phase alloy.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0007] The following detailed description makes reference to theaccompanying drawings in which like numerals designate like elements andin which:

[0008]FIG. 1 schematically illustrates an exemplary liquid phasesintering method.

[0009]FIG. 2 shows a cross section of an exemplary charge used in theliquid phase sintering method of FIG. 1.

[0010]FIG. 3 shows an exemplary temperature versus time plot for acharge indicating the temperature profile in the charge during theliquid phase sintering method of FIG. 1.

[0011]FIG. 4 shows a cross section of an exemplary rotating apparatusused in the liquid phase sintering method of FIG. 1.

[0012]FIG. 5 shows an exemplary embodiment of a charge and a heatingelement for a liquid phase sintering method with zone heating.

[0013]FIGS. 6a and 6 b show micrographs of a tungsten heavy alloy after(a) solid state sintering and (b) rapid liquid phase sintering accordingto the exemplary method, respectively.

DETAILED DESCRIPTION

[0014]FIG. 1 schematically illustrates an exemplary liquid phasesintering method for a two-phase alloy. The method 100 comprises forminga green body billet of a two-phase alloy 102, solid state sintering(SSS) the green body billet 104, forming a charge 106 by surrounding thesolid state sintered billet by a refractory barrier medium within arefractory container, wherein the refractory barrier medium preventscontact between the solid state sintered billet and the refractorycontainer, optionally flowing wet hydrogen through at least a portion ofthe charge 108, equilibrating a temperature of the charge below asolidus temperature of the two-phase alloy 110, changing the temperatureof the charge to a liquid phase sintering temperature of the two-phasealloy 112, maintaining the liquid phase sintering temperature for aperiod of time of less than or equal to four hours 114, optionallyrotating the charge about an axis of symmetry 116, optionally zoneheating 118 a portion of the charge to liquid phase sinter the two-phasealloy, reducing the temperature of the charge to less than the solidustemperature of the two-phase alloy 120, and optionally holding thecharge stationary as the temperature passes through the solidustemperature 122.

[0015] Forming the green body billet can be by any suitable method. Forexample, a green body billet can be cold pressed to about 50-60%, orhigher, theoretical density. The shape of the green body billet can beany suitable shape such as a solid shape, a hollow shape, or a shapecontaining both solid and hollow sections. For example, the shape of thegreen body billet can be a solid geometric form, both regular andirregular, or the shape can have one or more hollows open to an outersurface of the green body billet.

[0016] Solid state sintering of the green body billet can occur at anysuitable temperature for the materials used. For example, WHA sinteringcan occur in a multistep process with a final step at approximately1400° C. for several hours, e.g., 8 hours. Theoretical densities of thesolid state sintered billet can be from 50 to 95% theoretical density orhigher, preferably greater than 80% theoretical density and mostpreferably greater than 90% theoretical density.

[0017]FIG. 2 shows an exemplary embodiment of a charge 200. The charge200 includes a refractory container 202 in which the solid statesintered (SSS) billet 204 of a two-phase alloy is placed. The SSS billet204 is surrounded by a refractory barrier medium 206, such that the SSSbillet 204 does not touch the refractory container 202.

[0018] The refractory container 202 can take any suitable form and canbe made of any suitable material. For example, the refractory container202 can be formed of a metallic materials. Exemplary metallic materialsinclude molybdenum (Mo) based alloys and tungsten (W) based alloys.Ceramic materials can also be used for the refractory container.

[0019] The refractory barrier medium 206 can function to provide abarrier between the refractory container 202 and the SSS billet 204,such that the SSS billet 204 does not contact the refractory container202. In addition, the refractory barrier medium 206 can be permeable tohydrogen, especially wet hydrogen, which can reduce oxides. Further, therefractory barrier medium 206 can function to constrain and/or mold theSSS billet when the two-phase alloy is above the solidus temperature.For example, the restraining function of the refractory medium canassist in maintaining the shape of the two-phase alloy during the liquidphase sintering portion of the method. If freestanding when heated abovethe solidus temperature, the two-phase alloy can undergo severe slumpingand ejection of liquid matrix from the bulk. In an exemplary embodiment,the refractory barrier medium can be a ceramic liner, a ceramic sand, anopen cell ceramic foam, or any suitable form that can meet one or moreof the functions of the barrier medium.

[0020] For example, the ceramic of the refractory barrier medium can beAl₂O₃, ZrO₂, MgO, or any other suitable oxide or combinations thereof.In a preferred embodiment, the refractory barrier medium is a ceramicsand formed of Al₂O₃. Al₂O₃ sand can be easier to remove from the chargeat the end of the liquid phase sintering method, and also allows wethydrogen atmosphere to permeate through and contact at least a portionof the SSS billet, preferably the entire surface of the SSS billet.Additionally, Al₂O₃ sand has a suitable grain size such that seepage ofliquid matrix during the liquid phase sintering process does not seepinto the sand. For example, a preferred Al₂O₃ sand has a grain size ofbetween −325 and 80 mesh. However, a uniform grain size is not requiredand a suitable distribution of grain sizes may be used.

[0021] The charge can be configured to allow wet hydrogen to contact atleast a portion of the SSS billet. The contact can be for any suitabletime, such as, for example, up to 12 hours or longer, depending on thesize of the SSS billet, the type and/or permeability to wet hydrogen ofthe refractory barrier medium, and/or the manner in which the wethydrogen is supplied to the charge.

[0022] For example, the refractory barrier material can be permeable toa wet hydrogen atmosphere. The refractory barrier medium can either bediffusively permeable, i.e., a blanket of wet hydrogen atmosphere incontact with the refractory barrier medium will defuse through and to atleast a portion of the SSS billet, and/or the wet hydrogen atmospherecan be forced to flow through the refractory barrier medium to contactthe SSS billet, such as wet hydrogen having a pressure of 3 to 4 psi.

[0023] The wet hydrogen atmosphere can be supplied to the charge by anysuitable means. For example, the refractory container can have one ormore inlets, connections, or other suitable openings or fixtures to portweight hydrogen atmosphere diffusively and/or at a specified pressureinto the interior of the refractory container. FIG. 2 shows the charge200 with a hydrogen inlet 208. Optionally, the hydrogen inlet 208 can belocated on the closure 210.

[0024] In the exemplary embodiment shown in FIG. 2, the refractorybarrier medium 206 completely fills the interior space of the refractorycontainer 202 and completely surrounds the SSS billet 204. Further, inembodiments in which the shape has one or more hollow sections, thehollow sections contain the refractory barrier medium to assist inobtaining a uniform temperature profile across a cross section of theSSS billet during the liquid sintering process, e.g., the refractorybarrier medium can be packed around the SSS billet and into any hollows,such as troughs, holes, cut-outs, and so forth, so that the refractorybarrier medium contacts all exterior surfaces of the SSS billet and/oris tightly packed about the SSS billet. Optionally, the refractorybarrier medium can surround only a portion of the SSS billet that is tobe liquid phase sintered and/or the refractory barrier medium can alsoonly partially fill the refractory container. However, partiallysurrounding the SSS billet or partially filling the refractory containercan result in voids which can allow seepage of matrix and/or slumping ofthe two-phase alloy during liquid phase sintering. The restrainingfunction of the refractory medium assists in maintaining the shape ofthe two-phase alloy during the process. For example, if freestandingwhen heated above the solidus temperature, the two-phase alloy canundergo severe slumping and ejection of liquid matrix from the bulk. Therefractory medium, such as an aluminum oxide sand, can serve to protectthe container as well as allowing hydrogen gas to contact the surfacesof the SSS billet and prevent the SSS billet contacting the refractorycontainer because liquid billet material can alloy with selectmaterials, such as molybdenum alloys of the refractory container.

[0025] The charge 200 can be an open vessel, i.e., open at one end, orcan be closed. As shown in the exemplary embodiment of FIG. 2, thecharge 200 has a closure 210 at one end. The closure 210 can includethreads 212 for cooperating with threads 214 on the refractory container202 to form a closed refractory container. Further, the closure 210 atan outer surface 216 can have a connection 218, such as a socket,threaded connection, bolt, and so forth, for connecting to a mechanicaldevice (not shown), such as a motor, for moving or imparting motion,rotation, or other motive force to the charge 200.

[0026]FIG. 3 shows an exemplary temperature versus time plot for acharge indicating the temperature profile in the charge during theliquid phase sintering method of FIG. 1. Temperature in the charge at astarting time is initially at a starting temperature (point A), which ischanged at a reasonable rate (Δ₁) to a first temperature T₁ (point B). Areasonable rate can be any suitable rate that does not unnecessarilyprolong the process, for example, the heating rate can be 50 to 60° C.per hour to a temperature of 750° C. and 30 to 40° C. thereafter.Temperature T₁ can be any suitable temperature below the solidustemperature (T_(solidus)) of the two-phase alloy. For example, T₁ can be20-40° C. below the solidus temperature. The temperature of the chargeis equilibrated at T₁ for a period of time, the equilibration period(t_(eq)). For example, the equilibration period can be approximately 6to 8 hours, depending on the size of the charge and the furnace. At theend of the equilibration period (point C), the temperature of the chargeis increased to a liquid phase sintering temperature (T_(LPS)) at asuitable rate (Δ₂). The rate of change (Δ₂) from the end of theequilibration period to T_(LPS) can be, for example, 40-400° C. per houror can occur over approximately 0.1-2 hours.

[0027] Liquid phase sintering (starting at point D) continues for aliquid phase sintering period (t_(LPS)) of less than or equal to fourhours. The liquid phase sintering period can vary depending on themedium of the two-phase alloy and on the size of the SSS billet and/orthe charge. For example, a larger SSS billet or charge can requireadditional time at the liquid phase sintering temperature to liquidphase sinter the two-phase alloy. Preferably, the liquid phase sinteringperiod is from 0.3-1.5 hours.

[0028] At the end of the liquid phase sintering period (point E), thetemperature of the charge is reduced to less than the solidustemperature of the two-phase alloy. A suitable rate of change (Δ₃) forthe reduction of temperature is 20-100° C. per hour or can occur overapproximately 0.2-4 hours. If the rate of change (Δ₃) is too fast, thetwo-phase alloy can have increased porosity. However, if the rate ofchange (Δ₃) is too slow, the two-phase alloy can have increased settlingof tungsten particles within liquid metal matrix. Further, the rate ofchange (Δ₃) to a temperature below the solidus temperature of thetwo-phase alloy can occur by suitable cooling methods including ambientcooling and/or forced cooling.

[0029] At the end of the process (point F), the two-phase alloy can beremoved from the charge for subsequent processing and/or use.

[0030] Tungsten heavy alloy (WHA) is a two-phase alloy or metal-matrixcomposite consisting of almost pure tungsten (W) grains surrounded by amatrix that consists of an alloy of tungsten with secondary elements,e.g., nickel (Ni), iron (Fe), and/or cobalt (Co). WHA can vary incomposition from at least 80-90 wt. % W to about 95 wt. % W and thebalance Ni, Fe and/or Co. In an exemplary embodiment, the two-phasealloy is a tungsten heavy alloy including ≦93 wt. % W. Further, the WHAcan optionally include a balance of at least one secondary elementselected from the group consisting of Ni, Fe, and Co. An exemplary WHAcomprises 90 wt. % W, 8 wt. % Ni, and 2 wt. % Co.

[0031] An exemplary WHA, such as tungsten heavy alloy formed of 93 wt. %W and the balance Ni, Fe, and Co that has been solid state sintered toabout 95% theoretical density, e.g., greater than 90%, can have asolidus temperature of 1475° C.±20° C. and a liquid phase sinteringtemperature of 1535° C.±20° C. The solidus temperature is thetemperature at which the components of the matrix, such as nickel, beginto melt. For a tungsten heavy alloy solid state sintered to 90%theoretical density, the solidus temperature is 1455° C.±20° C.

[0032] As depicted in FIG. 2, the charge 200 has a cylindrical shapewith an axis X-X′ in the height dimension. However, the charge can haveany form with an axis of symmetry about which the charge can be rotatedduring an optional rotation step of the method. For example, when thecharge is cylindrical shaped, the charge can be rotated about the axisof symmetry X-X′ by a suitable rotating apparatus. Alternatively, thecharge can be rotated about the axis of symmetry Y-Y′ by a suitablerotating apparatus. Other suitable forms for the charge include asphere, a cone, a box, or other suitable form that has an axis ofsymmetry about which rotation can occur in a suitable rotatingapparatus.

[0033]FIG. 4 shows an exemplary rotating apparatus 400 for use in themethod of FIG. 1. As shown, the rotating apparatus 400 places the charge402 (shown in cross section corresponding to section A-A in FIG. 2) incontact with rotating bars 404 seated in notches 406 of support blocks408. A motor or other means of imparting motive force (not shown) can beattached to the charge 402 by way of the connection on the closure(shown in FIG. 2 as connection 218). For example, a bar can connect themotor and the charge via the socket in the closure. In other respects,the charge can include a SSS billet 410, a refractory barrier medium412, a refractory container 414, and a hydrogen connection (not shown).

[0034] Rotation (ω) of the charge 402 can occur in any direction aroundany axis of symmetry, such as clockwise or counter clockwise around axisX-X′. Rotation can be from one to several cycles per minute to limitcentrifugal forces acting on the particles and to limit the settling dueto gravity. The exemplary method of FIG. 1 can optionally includerotating the charge during at least a portion of the method during whichthe temperature of the charge is above the solidus temperature, e.g.,during the portion of the temperature-time profile represented in FIG. 3between points D and E. Such rotation can limit settling of the tungstenwhich is surround by liquid matrix alloy and also can assist incompositional uniformity. However, the charge can also be maintained ina fixed position during the period of time the charge is above solidustemperature.

[0035] Further, when the charge has been rotated during at least aportion of the method during which the temperature of the charge isabove the solidus temperature, the charge can be held stationary as thetemperature passes through the solidus temperature. For example, duringthe reduction of temperature from the liquid phase temperature to theend of the process, e.g., during the portion of the temperature-timeprofile represented in FIG. 3 between points E and F, the charge can beheld stationary during the time when the temperature passes through thesolidus temperature (T_(solidus)). The period of time during which thecharge is held stationary can be any suitable time, for example, thecharge can be held stationary within a temperature range of ±5°preferably ±2°, about the solidus temperature.

[0036] The temperature of the charge during any point of the exemplaryprocess, can be equilibrated, changed, or maintained by suitable methodssuch as radiative heating, resistive heating, or electromagneticheating. Exemplary electromagnetic heating methods include radiofrequency (RF) heating or microwave (MW) heating.

[0037] The charge can be heated in any suitable environment. Forexample, the charge or the charge in the rotating apparatus can beplaced within a furnace to achieve the desired temperature profileduring the method. Suitable furnaces include partial vacuum furnaces andatmospheric furnaces.

[0038] An exemplary method of liquid phase sintering can optionallyinclude zone heating a charge or a portion of a charge to liquid phasesinter the two-phase alloy. Zone heating can include heating the portionof the charge to the liquid phase sintering temperature to form aheating zone and traversing the heating zone from a first end of thecharge to a second end of the charge by relative motion between thecharge and a heating element. The temperature profile produced in theportion of a charge is sufficient to liquid phase sinter a two-phasealloy. For example, the temperature profile presented and described withreference to FIG. 3 can be applied to a charge or portions of a chargewith a WHA SSS billet and the heating element can traverse the geometryof the charge. Zone heating can occur both alternative to and incombination with rotating the charge about an axis of symmetry.

[0039]FIG. 5 shows an exemplary embodiment of a charge and a heatingelement for a liquid phase sintering method with zone heating. As shownin FIG. 5, a zone heating apparatus 500 includes a heating element 502positioned about a charge 504. Examples of heating elements include aninductively, resistively, radiatively or electromagnetically heatedring, jacket, coupling, sleeve, or other heating element that can beplaced around or approximate to a portion of the outer surface of thecharge and that can produce a suitably constrained heating zoneprojected toward the charge to achieve, within a two-phase alloy locatedin a charge, at least the liquid phase sintering temperature of thetwo-phase alloy. Preferably, the heating element is heated by anelectric resistance furnace or an induction furnace. In the exemplaryembodiment, the charge 504 is cylindrical and the heating element 502 isan inductive ring about the circumference of the cylindrical charge 504.

[0040] In the exemplary embodiment depicted in FIG. 5, the charge 504includes a 90% dense SSS billet 506 constrained vertically within arefractory container 508 and surround by a refractory medium 510. Thecharge 504 is heated by the heating element 502, which is depicted as aninductive coil, so as to melt a heating zone 512 at a first end 514 ofthe charge 502. As shown, the heating zone 512 is disc-like and isapproximately 10 centimeters or less in height. The heating zone 512 isthen moved up the charge 504 toward a second end 516 by movement of thecharge 504 and/or the heating element 502.

[0041] Relative motion can occur between the charge 504 and the heatingelement 502 such that a temperature profile in the charge 504 iscontrolled and the solidifying front of the liquid phase sinteredmaterial is moved uniformly toward a free surface of the two-phasealloy, e.g., toward an end of the two-phase alloy. Movement of theheating zone 512 can be coordinated with achieving a desired peaktemperature within the charge and relative motion can occur either stepwise or continuously. Once the heating zone 512 at any one portion ofthe charge completes the liquid phase sintering time period, the heatingelement is moved relative to the charge by either moving the heatingelement, the charge, or both. For example, the heating zone can be movedfrom a first end 514 of the charge 504 to a second end 516 of the charge504 by any suitable means, such as by a mechanical arm, a conveyorsystem, a stepper motor, and so forth. Further, the charge can bestationary or can also be moved through the heating zone by a suitableelevating or conveying system.

[0042] The rate of movement of the heating zone, and thus of thetemperature profile, can depend upon the size of the part and theheating system. Traverse rates in the range of about 1-5 centimeters perhour can be used to achieve melting and solidification gradients in theheating zone to achieve the desired compositional and mechanicalresults. Solidification gradients in the range of 50-200° per hour arepreferred in order to avoid generation of porosity defects in thematerial.

[0043] The moving heating zone can eliminate both defects caused byconventional methods, e.g., leakage and settling. For example, movementof the temperature profile toward a free surface can avoid shrinkagedefects within the two-phase alloy, e.g., an ingot of tungsten heavyalloy, formed by the liquid phase sintering process. Further, the sizeof the heating zone, e.g., cylindrical with less than 10 centimeters inheight depending on the thickness of the charge and/or solid statesintered billet in the transverse direction, and the rapid movement ofthe solidifying front, e.g., 1 to 5 centimeters per hour, can result ininsufficient time for any significant tungsten green settling. Also, thedirectional solidification of the moving zone can sweep shrinkage orevolved gas porosity up the ingot to the free surface of the top,thereby reducing porosity to less than or equal to 5%, preferably lessthan or equal to 2%.

[0044]FIGS. 6a and 6 b show micrographs of a tungsten heavy alloy after(a) solid state sintering and (b) rapid liquid phase sintering accordingto the exemplary method, respectively. The photomicrograph in FIG. 6ashows porosity distributed throughout the image. This porosity isapproximately 5%. Further, the tungsten phase (the light shaded phase)is contiguous and the matrix material (the dark gray phase) is notcontiguous. The contiguous tungsten phase, which has low ductility, cannegatively impact crack propagation within the material.

[0045] The photomicrograph in FIG. 6b shows that the tungsten phase hasripened into substantially spherical phase regions. Further, the matrixmaterial, e.g., nickel, iron and/or cobalt, has an increased contiguouscharacter, e.g., a larger proportion of the matrix material iscontiguous than in the solid state sintered sample of FIG. 6a, and theporosity is not evident. Accordingly, the increase in proportion matrixmaterial that is contiguous improves the ductility of the liquid phasesintered two-phase alloy. As shown, the tungsten phase is approximately50 microns in diameter. Also, FIG. 6b shows that at least a portion ofthe tungsten phase is not contiguous or is completely surround by matrixphase, e.g., does not contact a neighboring tungsten phase.

[0046] While the present invention has been described by reference tothe above-mentioned embodiments, certain modifications and variationswill be evident to those of ordinary skill in the art. Therefore, thepresent invention is to be limited only by the scope and spirit of theappended claims.

What is claimed is:
 1. A method to liquid phase sinter a two-phasealloy, the method comprising: forming a green body billet of a two-phasealloy; solid state sintering the green body billet; forming a charge bysurrounding the solid state sintered billet by a refractory barriermedium within a refractory container, wherein the refractory barriermedium prevents contact between the solid state sintered billet and therefractory container; equilibrating a temperature of the charge below asolidus temperature of the two-phase alloy; changing the temperature ofthe charge to a liquid phase sintering temperature of the two-phasealloy; maintaining the liquid phase sintering temperature for a periodof time of less than or equal to four hours; and reducing thetemperature of the charge to less than the solidus temperature of thetwo-phase alloy.
 2. The method of claim 1, wherein solid state sinteringthe green body billet results in at least 80% theoretical density. 3.The method of claim 1, wherein the refractory barrier medium is aceramic liner, a ceramic sand, or an open cell ceramic foam.
 4. Themethod of claim 3, wherein the ceramic sand is Al₂O₃, ZrO₂, or MgO. 5.The method of claim 3, wherein the ceramic sand has a grain size of −325to 80 mesh
 6. The method of claim 1, wherein the refractory container isformed of a metallic material.
 7. The method of claim 6, wherein themetallic material is a Mo-based alloy or a W-based alloy.
 8. The methodof claim 1, wherein the refractory barrier medium is permeable to a wethydrogen atmosphere and the method comprises flowing wet hydrogenthrough at least a portion of the charge.
 9. The method of claim 8,wherein the wet hydrogen atmosphere contacts at least a portion of thetwo-phase alloy.
 10. The method of claim 8, wherein the wet hydrogen hasa pressure of 3 to 4 psi.
 11. The method of claim 1, whereinequilibrating a temperature of the charge below a solidus temperature ofthe two-phase alloy is equilibrating at less than 20° C. below thesolidus temperature.
 12. The method of claim 1, wherein changing thetemperature of the charge to a liquid phase sintering temperature of thetwo-phase alloy is changing the temperature at a rate of from 40° C./hrto 400° C./hr.
 13. The method of claim 1, wherein the period of time formaintaining the liquid phase sintering temperature is from 0.3 hours to1.5 hours.
 14. The method of claim 1, wherein reducing the temperatureof the charge to less than the solidus temperature of the two-phasealloy is reducing the temperature at a rate of from 20° C./hr to 100°C./hr.
 15. The method of claim 1, wherein the two-phase alloy is atungsten heavy alloy.
 16. The method of claim 15, wherein the tungstenheavy alloy includes less than or equal to 93 wt. % tungsten.
 17. Themethod of claim 15, wherein the tungsten heavy alloy includes less thanor equal to 93 wt. % tungsten and the balance at least one secondaryelement selected from the group consisting of Ni, Fe and Co.
 18. Themethod of claim 15, wherein the solidus temperature is 1475±20° C. 19.The method of claim 15, wherein the liquid phase sintering temperatureis 1535±20° C.
 20. The method of claim 1, wherein the charge has an axisof symmetry and the method comprises rotating the charge about the axisof symmetry during at least a portion of the method during which thetemperature of the charge is above the solidus temperature.
 21. Themethod of claim 20, wherein a rotation rate of the rotating charge isfrom 1 to several cycles per minute.
 22. The method of claim 1, whereinthe charge has a cylindrical shape with an axis in a height dimensionand the method comprises rotating the charge about the axis of symmetryduring at least a portion of the method during which the temperature ofthe charge is above the solidus temperature.
 23. The method of claim 22,wherein a rotation rate of the rotating charge is from 1 to severalcycles per minute.
 24. The method of claim 1, comprising holding thecharge stationary as the temperature passes through the solidustemperature during the step of reducing the temperature of the charge toless than the solidus temperature.
 25. The method of claim 1, whereinthe charge is placed in a partial vacuum or an atmospheric furnace. 26.The method of claim 1, wherein the temperature of the charge isequilibrated, changed, or maintained by radiative heating, resistiveheating, or electromagnetic heating.
 27. The method of claim 26, whereinelectromagnetic heating includes RF heating or MW heating.
 28. Themethod of claim 1, comprising zone heating a portion of the charge toliquid phase sinter the two-phase alloy.
 29. The method of claim 28,wherein zone heating comprises heating the portion of the charge to theliquid phase sintering temperature to form a heating zone and traversingthe heating zone from a first end of the charge to a second end of thecharge by relative motion between the charge and a heating element. 30.The method of claim 29, wherein the relative motion is step-wise orcontinuous.
 31. The method of claim 29, wherein the relative motion isat a rate of 1 to 5 cm per hour.
 32. The method of claim 28, whereinzone heating occurs during the step of changing the temperature of thecharge to a liquid phase sintering temperature of the two-phase alloy.33. The method of claim 28, wherein the charge has an axis of symmetryand the method comprises rotating the charge about the axis of symmetryduring at least a portion of the method during which the temperature ofthe charge is above the solidus temperature.
 34. The method of claim 33,wherein a rotation rate of the rotating charge is from 1 to severalcycles per minute.
 35. The method of claim 28, wherein the charge has acylindrical shape with an axis in a height dimension and the methodcomprises rotating the charge about the axis of symmetry during at leasta portion of the method during which the temperature of the charge isabove the solidus temperature.
 36. The method of claim 35, wherein arotation rate of the rotating charge is from 1 to several cycles perminute.